Low pass filter for B&W?

If you are shooting black & white film and have to limit yourself to only 1 filter then choose the Yellow. It helps with the contrast and doesn't affect the rest of the rest of the scene very much. A Red filter would be used to darken the sky or make green foliage darker or anything red in the scene lighter. A Green filter would be used to lighten green foliage or to darken anything red in the scene.

If you are shooting color film or digital, the only filter you need is a polarizer. The polarizer will darken a blue sky and can be used to remove glare and/or reflections from water, glass, white sand and painted metal - but not polished metal like chrome or stainless steel.

Of course, every lens you own should have a good quality Haze/UV filter mounted to protect the front element of your lens.

First af all, a clarification: a low pass filter has nothing to do with color filters. A low pass filter is built-in in most cameras to filter some spatial frequencies so as to avoid Moire patterns.

A color filter is used in front of the lens to block frequencies of the visible spectrum, thus intensifying certain colors.

Its selection would depend on what you intent shooting, for example if you are shooting landscapes with lots of green, you would be better off with only the yellow, or if your shooting water and blue skies you would need only the red one to intensify the contrast.

Personally I believe you don´t really need any filters at all in the digital era. Why throw away any information with a filter when you can open the photo in Photoshop and apply any color filter you want, even more than one on each photo?

I presume this is for film, then you're talking about the degree by which Blue light is held back. Yellow not much, Orange a lot more, Red if you want 'Gothic'. A polarizing filter is adjustable between the Yellow and Orange effects on a bright sunny day.

If your shooting digital then just shoot colour and convert in Photoshop or similar, then all your options are open to you and everything in between.

Chris